High-voltage battery packs are constructed by co-packaging a number of individual battery cells or modules, and interconnecting the positive and negative terminals of the cells or modules in a series or series-parallel arrangement. Lithium-ion batteries are particularly attractive for such applications because of their low weight and high power density, and because of their relatively high cell voltage, which minimizes the number of terminal connections in the battery pack.
To minimize cost, individual lithium-ion battery cells can be manufactured in the form of a soft package with metal foil terminals, as illustrated in FIG. 1. Referring to FIG. 1, the cell 10 has laterally-staggered aluminum-foil and copper-foil terminals 12 and 14, and is sealed in an envelope 16 of metalized plastic.
Although two or more foil battery terminals can be electrical joined by ultrasonic welding (high temperature welding processes are impractical due to the plastic cell construction), pressure connections are generally preferred so that failed or damaged cells of the battery pack can be replaced with new cells. For example, the patent document WO 2007/107036A1, published on Sep. 27, 2007, shows a soft package lithium ion battery pack 1 in which the foil terminals 4 of individual battery cells 3 are bolted to bus bars 2. However, bolted pressures connections such as those shown in the aforementioned patent document can be problematic for several reasons, including galvanic corrosion due to joining dissimilar metals, open-circuiting due to loose connections, and short-circuiting due to stray mounting hardware. Additionally, bolted pressure connections concentrate the battery current over a relatively small portion of the terminal area. Accordingly, what is needed is a pressure connection apparatus that more efficiently and more reliably interconnects the metal foil terminals of soft package battery cells within a battery pack.